templatetags: adapt |length and |length_is for lazy variables (#49383)

tests/test_formdata.py

@@ -1250,6 +1250,25 @@ def test_lazy_variables_missing(pub, variable_test_data):
             assert context['form_var_foo_foo_xxx'] == 'bar'
 
 
+def test_lazy_variables_length(pub, variable_test_data):
+    formdef =  FormDef.select()[0]
+    formdata = formdef.data_class()()
+    formdata.just_created()
+    formdata.data = {
+        '0': 'bar',
+        '6': '3',
+    }
+    pub.substitutions.reset()
+    pub.substitutions.feed(formdef)
+    pub.substitutions.feed(formdata)
+    for mode in (None, 'lazy'):
+        pub.substitutions.reset()
+        pub.substitutions.feed(formdata)
+        assert WorkflowStatusItem.compute('{{ form_var_foo_foo|length }}') == '3'
+        assert WorkflowStatusItem.compute('{% if form_var_foo_foo|length_is:3 %}ok{% endif %}') == 'ok'
+        assert WorkflowStatusItem.compute('{% if form_var_foo_foo|length_is:form_var_foo_foo_baz_baz %}ok{% endif %}') == 'ok'
+
+
 def test_lazy_map_variable(pub, variable_test_data):
     formdef = FormDef.select()[0]
     formdata = formdef.data_class().select()[0]

wcs/variables.py

@@ -665,6 +665,13 @@ class LazyFieldVar(object):
     def __mul__(self, other):
         return self.get_value().__mul__(other)
 
+    def __len__(self):
+        return len(self.get_value())
+
+    def __int__(self):
+        return int(self.get_value())
+
+
     def startswith(self, other):
         return self.get_value().startswith(other)